The present invention generally relates to methods and apparatuses for rapidly making a quantitative determination of bacteria present in water. More particularly, the invention relates to methods and apparatuses for rapidly making a quantitative determination of bacteria present in water such as wastewater effluent, fresh water or sea water by bacterial adenosine triphosphate (ATP) or iron porphyrin assay.
A rapid and routine procedure for a quantitative determination of bacteria present in water is frequently of vital importance, particularly when the determination relates to the quality of a community water supply and a determination is required to be made within a few hours. No prior art technique is capable of giving such a determination in less than a day nor are they suitable for automation.
The present technique for the quantitative determination of bacteria in water, employed for many years, is the colony count, which takes approximately 24 hours to complete. This technique is used for testing wastewater effluent, river or lake bacterial contamination, estuary condition, bay water and the like.
The colony count technique involves the filling of a Petri dish with agar containing a medium considered suitable for the growth of bacteria assumed to be present. Such a medium is trypticase soy agar. Escherichia coli is generally the principal coliform commonly found in water contaminated with fecal material. Pseudomonas aeruginosa and Alcaligenes faecalisare are also commonly found in wastewater effluents. In practice, agar, in powdered form, is mixed with trypticase soy, also in powdered form, with an appropriate amount of water and autoclaved. The broth is then poured out into a number of Petri dishes and allowed to cool until the broth solidifies.
A small sample of the water being tested is streaked on to a dish. This is repeated with a plurality of serial dilutions of the sample in orders of magnitude of 10. With such a procedure a dilution is achieved which is amenable to being counted and at the same time can be related to a given volume of sample.
The colony counting technique is useful with respect to counting bacteria in a salt water environment. Some complications, however, must be taken into account. Sea water supports a great deal of bacteria. However, most bacteria contained in a typical sewage environment are not viable in water with a high saline content, but they are not killed instantaneously. The colony counting technique, therefore, will only confirm how many viable cells are present in the salt water sample that are supported by the particular growth medium employed.